Telephone system



- sept 25, ma' 1368,5,410

R. F. STEHLIK TELEPHONE SYSTEI Filed Nov. 3. 1926 2 sheets-Shut 2 F'iq: E

' EuduzFh E srhhk f 30Y in the case lof rota? Patented Sept. 25, 1928 uN-Vrin) STATES 1,685,419 PATENT OFFICE-.-

RUDOLPH E'. sTEHLrx, OE cHIcAGo, ILLINOIS, AssIGN'OR' To AUTOMATIc': ELECTRIC INC., OE CHICAGO, ILLINOIS, A CORPORATION OE DELAWARE. Y

TELEPHONE SYSTEM.

Anp-punti med, mvi'mbr 3) 192. senin No. 145,945.

The invention relates to telephone systems in general, but is more particularly concerned .with telephone systems in which non-numerical preselectors or lineswitches are used to I automatically connect lines of one group to idle. trunk lines of another group. The principal object of this invention is the produc*- tion of new and improved control circuits for a group of lineswitches for use in a system l of this kind n f v A feature of this invention is that vall the individual line relays ofthe lineswitchesY of'a group have been dispensed With, anda group of common line relays, considerably less in l number than the number of linesWitches in the group, is substitutedtherefor. Thus, a material saving isA effected in the total number oflline relays necessary for a given number of lineswitches. Y 4 ,Y l Linesivitclies of the more common types, `in which'individual line relays are` provided -,for each lineswitch, have the inherent objection able characteristic that under certain conditions two linesivitches of the same groupmay operate to connect t-he tWo lines terminating in these linesvvitches to the same trunk line. This condition occurs Whenever the plungers or Wipers of tvv-o lineswitches (plungers in the case of plunger type lineswitches and Wipers type lineswitches) are Vstanding opposite t e same Vidle trunk line, and are operated simultaneously or very nearly so. Accordingv to another feature'of this invention, the possibilityunder any condition of t-Wo lines being connected to the same idle trunk line is entirely eliminated. I y r The object and the features of the invention will be described in detail in thefollowing specification with the aid of theV annexed drawingscomprising Figs. 1 andr which illustrate by means of the usual circuit `diagrams one embodiment of the invention as a plied to a group of25 primary lineswitches oi) the plunger type used in an kautomatic eX- change, although the invention is in no Way limited to any particular kind of lineswitch or to there being any particular number of lineswitchesin agroup. y l Y Referring to the drawings, -at the top of Fig 1, subscribers line comprising'conduc- Y tors 6221116164, terminating atthe cent-ral eX- change in the linesWitchLSgis shown, and at the bottom of Fig, 1, a subscribers line comprising conductors 62 and 64', terminating at the central exchange in the lineswitch LS, is shown. Thel lineswitches LS52 and LS34 together With the other linesWitches of the group have common access in their banks toa group ofpgtrunk lines, one of which is shown comprising conductors 72, 73, and 74. Each trunkline terminates in an automatic svvitch (not s hovvn) suchl as a first selector sw'itch'of the Strowger type. .v Meclianically, the ylinesvvitches are of the Well known plunger typehaving plungers which control r the connection ot the subscribers line-With an idle trunk line, the usual individual line relays having been dispensed with. In this type of lineswitch the operat ing magnet has two armatures and two windings. One armature supports the plunger andvhen operated, plunges the plunger into the lineswitch bank; the other armature When operated disconnects the line relay connections from theline conductors (said connecvtions described in detail in later paragraphs). The Winding referred to hereinafter as the holdingY winding or .bridge-cut-OH Windin when energized, roduces sufiicientyma netic gull to operate t e vlatter varmature on y, or

old both armatures operated if they are already oprated Whenl this Winding is energized VThe* Winding referred tohereinafter asthe pull-down Winding, When energized, 'produces' sufficient magnet-ic pull to operate both armatures, The plungers of the lineswitches are further controlled by a common master switch inr such a manner that the plungersV of all the idle lineswitehes of the group are always'standing opposite an idle trunk.

A gro up of common'line relays substituted for the individual line relays, .controls the battery and ground connections to the pulldown windings of the operating magnets of all the lineswitches of the group. This group of common line relays with otherl auxlliary relays isshown in the middle of Fig. 1 in tWoroWs. y u l To most clearlydescribe the connections of the group ofcommon line yrelays with `the conductors ofthisgroup of 25 lines, the 25 lines are assumed to be divided into Yfive subgroups.` Each line is designated by!!I numeral of two digits, the tens digit desig- 1 nating the subgroup containinr the line, and Ythe units digit designating t e particular line in that subgroup. In Fig. 1", the upper roW of line relays, namely relays 210, 220, 230, 240, and 250, are the subgroups of tens )l0 designating line relays one being provided `for each subgroup and designated to correspond therewith; the loWer rovv of line relays, namely, relays 301-305, inclusive, are units designating line relays.V One conductor of each ot the lines of each subgroup is connected to the tens line relay Whose tens designating vdigit is the same as that of the subgroup. The other conductor of each line is connected to the units line relay having the same units designation as the line. For eX- ample, one conductor of each of the lines numbered 51-55, inclusive, isV connected to tens line relay 250 by Way oi common ktens marking conductor-a5. Conductor 62 of the line terminating in linesivitcli LS, this line being line No. 52, is one or these. Further# incre, one conductor of each of the lines numbered 12, 22, S2, i2, and 52 is connected to units line relay 302 by Way of common units marking conductor Z22, conductor 6a of line No. 52 te 1minating in linesWitch L85? being one otthese; Thus,`one conductor ol each line is connected to a certain tens line relay and the other conductor is connected to acertain-units line relay,1but the two conductors erating magnets ci' the Grou ot' tivcnt -ve 2D D lineivitches, including magnet 52 of linesvvitch LS52 and magnet 34 of linesvvitch LSM. The numerical designation of each magnet Vcorresponds With the number of the line terminating in the linesivitcli With'rivhich the magnet is associated. Y The magnets have been shown arrangerL so as to most con-Veni# ently show the circuit connections of their pull-down windings as controlled by the separate line relays.V 'lheniagnets associated with the lines of each subgroup appearin one horizontal roiv with the subgroup `or tens marking line relay, to which one conductor olf each Aol the lines ofV that subgroup is connected, :directly to the lei't. The magnets vof each row are arranged in numerical order. so that magnets with the saine units designation appear in the same vertical row.

Y AEach units line relay, to which one conductor of leach ot vthe lines having the saine Yunits 'designation is connected, appears 'directly underneath the vertical .row of magnets associatedwith theselines. A

VThe connections between the common line Vrelays and the operating magnets ot the linesWitches are such that When a call is initiated over a certain line, the particular units line relay to Which one conductor of the calling `line Ais connected is operated to connect battery potential to one terminal of the pullcuit traced above.

nected is operated to prepare the connection of ground potential to the other terminal of the pull-down Winding or' all rthe operating magnets in the associated horizontal row which also includes the operating magnet of the calling line. Thus, the circuit for the pull-down Winding of the operating magnet of the calling line is established, Which magnet operates and effects the operation of the linesivitch to connect the .calling line to an idle trunk. Y

VTo further describe theinvention, a detailed description of the operation of a linesivitch in extending a connection from a subscribers line to an idle trunlrline ivill'be given. Forthis purpose,referring toFig. 1, it Will be assumed that the subscriber on the line comprising `conductors 62 and 6e removes his receiver to initiate a call. Responsive thereto, a bridge is closed across the line conductors Which closes a circuit which may be traced :trom ground by Way of resting con tact and Varmature 111,'armature 95and the resting contact, common tens marking conductor a5, individual tensmarlring conductor 125, armature 65 and the resting contact, line conductor 62,' over the bridge at the-,calling substation, line conductor resting contact and armature 66, individual units marking conductor 122, common units marking conductor b2, resting Contact and armature 102, the common units line relay 302 to battery. Relay 302 operates and performs the tollow ing circuit changes: At armatures 312, 332, 334, and 352, battery potential is connected through resistance 113 to the lower terminals of the pull-down'WindingV of magnets 12, 22, 32, 12 and 52 ot the corresponding lineswitches, respectively'. (See Fig. 2.) kAt armature 362 the initial energizing circuit i'ior relay v302 is opened by separating the normally closed contact-s controlled by this armature, and alocking circuitisfclosed for this relay inseries with relay and`100, which circuitmay be traced from ground by Way Vot the resting Contact and armature 111, through the Winding'ot relay 90, through the Winding of relay 100, armature l'and the resting contact, armature 362 and the Working contact through the Winding oi relay 302 to battery. At armature 372 a circuit is prepared which will be described presently.

Both relay 90 and 100 energize in the cir- Relay 100, in operating, disconnects the upper terminals ol relays 301-305 from the common conductors lil-$5 at armatures 10i-105 respectively, and at armature 106 closes the circuit for relay 110. Relay 110, by reason of itssloW-acting characteristic, does notoperate its armature 111 until an appreciable time after its circuit is closed. Relay 90, in operating, removes the normal short circuit around relay 210, 220, 230, 2110, and 250, at armatures 91, 92, 93, 94, and respectively. Tens line relay 250 now operates over the circuit from ground by way known manner.v and connects ground of thel resting contact and armature. 111, through the Winding of relay 250, armature 8,5` and the resting contact, conductor a5, con-` ductor 125, armature and Vthe resting contact, line conductor 62, over the bridge at the callingsubstation, line conductor 64, rest-ing contact and armature 66, conductor b2, armature 3'72 and the working contact through resistance 112 to battery. Relay 250, in operating its armatures 251-252, prepares a circuit for connecting ground potential to the upper terminals of the pull-down'winding of operating magnets 5155 of the corresponding lineswitches, respectively, (see Fig. 2). At armature 256 relayl 250 closes a locking circuit Jfor itself which may be traced from ground by way ofthel resting contact and armature 111, through the winding of relay 250, working contact and armature 256, resting contact and armature 246, resting contact andv armature 236, resting contact and armature 226, resting contact and armature 216, through the winding of relay to battery.

Relay 80 also operates over this circuit and at armatures 81-85 disconnects common conductors @1 -a5 from the upper terminals of relays210, 220, 230, 240, and 250, respectively, and at armature, 86 completes the circuit for placingV ground potential on the upper terminal of the pull-down winding of magnets 51--55,"inclusiv.e. With both relays 80 and operated, the line relays are disconnected from all the lines of the group. Therefore no other line can initiate a call at this particular time. f

Since ground. potential, has now-been connected to upper terminal of the pull-down Winding of magnet 52, and battery potential through resistance 113 has been connected to the lower terminal of this Winding, magnet 52 e-nergizesv and operates the plunger (not shown) which causes springs 67, 68, 69', and 7.0 to close, thereby extending the connect-ion by way of trunk conductors, 72, 73, and 74 to the first selector switch terminating this trunk. In operating, magnet 52 also disconnects the line conductors 64 and 62 from the tens marking conductor a5 and the units marking conductor b2 armatures65 and 66, respectively. By the closure of springs 69, groundpotential is applied to conductor 75 connected to the bankv Contactin the master switch bank associated with the trunk comprising conductors 71, 72, 7 3, and 74, which causes the master switch to operate and position the plungers of all the idle lineswitches of this group opposite the next idle trunk. Thisoperation is well known to those skilled in kthe art andconsequently need noty be `further described.

As a result of the extension of the connection to the selector switch terminating the trunk comprising conductors 72, 73, and 74. this selectorswitch operates in the Well poential to the release conductor 73, thereby` closing a holding circuit for the holding Winding of magnet 52 to hold this relay operated and hold the plunger in operated position, and also apply ground potential to the private normal conductor 63 to mark the subscribers line busy. Y

The slow-acting characteristic of relay 110 is so timed that it does not operate its armature 111 until after all the foregoing operations described after its circuit was closed at armature 106, have taken place, that is, until after the selector switch terminating in the trunk comprising conductors 72, 7 3, and 74 has had time to complete a holdin(y circuit Afor magnet 52 by the application olP ground potential to the release conductor 7 3, and the master switch has performed its operation. As soon as these operations have taken place, however, relay 110 operates its armature 111 thereby opening the holdingveircuit for relays 250, 90, 100, and 302. These relays will thendeenergize and restore their armatures to normal. Relay 100, in deenergizin also opens the circuit of relay 110 which a so deenergizes a short time thereafter and restores armature 111 to normal. The common line relay equipment is now ready to take care of another call. Further extension of the connection will take place in the well known manner.

VlrVhen the calling subscriber replaces his receiver atrthe termination of a conversation, the first selector is released in the well known manner, disconnecting groundpotential romthe release conductor 73, thereby opening the holding circuit for magnet 52 and also marking the line at substation to thecalling substation idle. Magnety 52 thereupon de'- energizes, restoring its armatures 65 and 66 to normal andralso releasing the plunger to separate springs 67 68, 69, and 70.

When theI subscriber on the line comprising-conductors 62 Yand 64 `initiatesfa call, magnet 34 of lineswitch LSA is operated similar to the way magnet 52 of the lino switch LS5-2was operated. In this case, units line relay 304Y is` operatedto .apply battery potential throughresistance 113 tothe lower terminals of the pull-downwindings of mag, nets 14, 24, 34, 44, and 54 at armatures 314, 324*` 334, and 354, respectively, and tens line relay 230 is operated to prepare a circuit for placing ground potential on the u per terminals'of the pull-down windings o magnets 31-35 at armatures 231-235, respectively. Magnet 34, in operating, operates the plunger ot the lineswitchfLSaf* which connects the'` subscribers line tothe trunk line opposite which the lunger is the call is initiated. l

, As previously stated. a special feature ofV the inventionis that the possibility offtwo lineswitches connecting their associated lines positioned at the time tothe sameftrunlz line is entirely eliminated.

example, itsmay beV assumed that the subscriber on line comprising conductors 62 and 6dr-, and the subscriber on line comprising conductors 62 and 6e', remove their re'- ceivers to initiate a call simultaneously. Upcn the removal of the receiver -at these substations,7a circuit is simultaneously `estabished for units line relay 302, and ,tor units line relay 304. Both relays 302 and st operate. Relay 302, appearing lirstin. the series, opensits initial energizing circuit and closes a holding circuit for itseli at the armature v862 in series with relays 100 and 90 as de-Y scribed previeusly. Relay 30a also operates its corresponding armature 364, opening the connection over the other-idle nected` to the same units line initialv energizing circuit by separating thev springs Vcontrolled. thereby. However, no holding circuit is closed Ytor relay 304C since armature 362 has separa-ted trom'its resting contact. Therefore relay lu-ideenergizes and remainsV deenergized until after its initialenergizing circuit is againclosed upon the deenergization of relay 100.y rlhis, as described above, does not take place until the subscribers line comprising conductors 62 and 64: has been connected withthe trunk line opposite-which the plungers have been stanclingand'tlie master switch is operated to move the remaining plungers opposite the nexty idle trunk. lll/*ith relaySOt in a deenergized state, no circuit can be closed for the operating magnet 34 ot lineswitch 'LSH at this time. The circuit of magnet 52 is closed, as previously described, however, causing linesw'itch LS to operate and connect its associated line to an idle trunk. After lineswitch LS52 has., operated andthe master switch has selected another idle trunk, re-

lays 90, 100, 80,*and y110 deenergize, alterV which the circuit of magnet 34 is closed to operate'lineswitch LS34 to extendthe second trunk line.

considered in lines are conrelay, remove their receivers simultaneously. For exanuile, it may be assumed that the subscriber on the Another case may now be which two subscribers, whose line comprising conductors 62 and 64 and the subscriber on the line whose operating magnet is magnet 42, removes their receivers simultaneously to initiate calls.

Vconnected to conductor Z22.

Conductor 64 l Lesage and one conductor ofthe latter line are both Conductor 62 is connected to conductor a5, while the corresponding conductor of the latter line is connected to conductor d4. lV hen the two subscribers remove their receivers, two parallel circuits are closed :tor relay 302, one circuit including conductors 62, 64, 122, ande2 in series as previously traced, and the other circuit including the two line conductors of the other calling' line, a conductor corresponding to conductor i22, and conductor b2 in series. Relay 302 operates as previously described, connecting battery potential through resistance lll to one terminal oiimagnet l2, 22, 32, 42, and 52, connecting battery potential through resistance 112 to conductor b2, and closing a locking circuit for itself in series with relays and 90. Relay 90, in operating, opens theshort circuit around relays 210, 220, 230, 2410, and 250. Both relays 250 and 2li() operate, relay 250 operating over a circuit including conductor i792, line conductors 62 and 6st, and conductor c5 in series, and relay`240 operating over a circuit including conductor b2, the two line conductors of the other calling line, and conductor 1:1 in series. Relay 240, in operating, prepares a circuit for connecting ground potential. to the other terminal of magnets tl-4:5 at armatures 24J- 245, respectively, and closes a liol'dingcircuit Jfor itseliC at armature 2&6 in series with relay 80. Relay 250,in operating,temporarily performs similar circuit-changes Abut does not-*close a locking circuit for itself at armature 256, since armature 246` has separated from its resting contact. Relay 80, in operating, opens the initial energizing circuits of both relays 24L-Oand 250 at varmatures 84 and 85, respectively. As a result, relay 250 deenergizes andr releases its armatures. t armature 86Y et relay 80, the circuit is closed for conneeting'ground potential tothe other terminals of magnets ll-i inclusive. lilith relay250 in a deenergized state, no circuit can be closed for the operating magnet 52 of lineswitch Llg atthis time. Since the circuit for magnet 42 is completed, however, lineswitch LSL2 `v(not shown) operates to extend vtheV connection to an idle trunk, after which the operated relays Vin the common line relay Vgroin? restore to normal. lmniediatelyv thereafter,` the common line relays function to cause thek operation of lineswitch LS52 as previously described.

From the ,foregoing examples, it is clear taat only one tens line relay and only one units line relay can be held energized at one time,

and consequently the circuit of only one operating magnet relay can be closed at one time.

lne

As a result, even though calls are initiated simultaneously, the lineswitches of the calling lines will not operate simultaneously but will operate in succession, the order of operation depending onthe position of the line relays with respect to the chain locking circuits of the line relays to which each calling line is connected.

This completes the description of the operation of the invention. lVhat is thought new and is desired to have protected by Letters Patent will be specifically stated in the appended claims.

Vhat is claimed is: p n

l. Iny a telephone system, a group of lines, a preselecting lineswitch terminating each of said lines, a group of'trunks, means in cach lineswitch for connecting the associated line to one of said trunks, and a group of line relays less in number than the number of lines in said group of lines for controlling the connecting means in all said linesvvitches. Y

2. In a telephone system, a group of lines, a lineswitch terminating each of said lines, a group of trunks, means in each lineswitch for connectingthe associated line to one of said trunks, a group of line relays less in number than the number of said lineswitches, means effective when a -call is initiated over any one of said lines for operating certain of said line relays to cause the operationl of the connecting means in the lineswitch terminating the calling line to connect the calling line with one of said trunks, and means for preventing the operation of any other line relays after certain of said relays have been operated, until after said calling line is connected to a trunk.

8. In a telephone system, a group of lines, a lineswitchterminating each of said lines, a group of trunks, means 1n each lineswitch for connecting the associated line to one of said trunks, a group of line relaysless in Vnumber than the number of said lineswitches, means effective when a call is initiated over any one of said lines for operatingcertaln of said line relays to cause the operation of the connect- .ing means in the line'switch terminating the calling-line to connect the calling line with one of said trunks, and means for preventing the operation of the connecting means in more than one linesyvitch at the same time When calls are initiated over two lines simultaneously or nearly so. Y

4. In a telephone system, a group of lines, a lineswitch terminating each of said lines, a group of trunks, means in each lineswitch for connecting the associated line to one of said trunks, amagnet in each lineswitch for controlling the connecting means, a battery, said magnet .being normally disconnected from the poles of said battery, and a group of line relays less in number than the number of magnets for controlling the connection of the poles of said battery to said magnets.

5. In a telephone system, a group of lines, a linesvvitch terminating each of said lines, a group of trunks, a magnet in each lineswitch :tor connecting the associated line to one of said trunks, the magnets of all of said lineswitches being divided into a plurality of'subi ticular primary line relay and Va particular' secondary line relay being normally connected to each line, and means effective When a call is initiated over one of Said lines for operating the primary line relay and the secondary line relay normally connected t0 thecalling line to cause the operation of the magnet of the lineswitch terminating the calling line.

6. In a telephone system, a group of lines, a linesivitch terminating each of said lines, a group of trunks, a magnet in each lineswitch for connecting the associated line to one of said trunks, the magnets of all of said line# switches being divided `into a plurality of subgroups, a primary line relay for each subgroup, a. secondary line relay for the corresponding magnets of each subgroup, means effective Whena call is initiated over one of said lines for operating one of said primary line relays and one of said secondary line relays to cause the operation of the ma net .of the lineswitch terminatingV the calling ine, and means for vitiating the effect of the operation of more than one secondary relay at one time even though calls are initiated over two of said lines simultaneously.

7. In a telephone system, a group of lines, a linesivitch terminating each of said lines, a group of trunksa magnet in each lineswitch for connectin the associated line to one of said trunks, t e magnets of all of said linesvvitches being divided into a plurality of subgroups, a primary line relay for each subgroup a secondary line relay for the corresponding magnets of each subgroup, means eifective when a call is initiated over .one of said lines for establishinginitial operating circuits for r one of said Vprimary line relays and for one of said secondary line relays to cause the operation of the magnet of the linesvvitch terminating the calling line, and means for closing holding circuits and for opening the initial operating circuits for the operated primary line relay andthe operated secondary line relay.'

8. In a telephone system, a group of lines, a lineswitch terminating each of said lines, a group of trunks, a. magnet in ea ch lineswitch for connecting the associated line to one of said trunks, the magnets of all of said linesvvitches being divided into a plurality of subgroups, a primarypline relay for each subgroup, a secondary line relay for the corresponding magnets of each subgroup, means effective when a call is initiated over one of said lines for establishing initial operating circuits for one of said primary line relays and one of said secondary line relays to cause the operation of the magnet of the lineswitch terminating the calling line, means for .closa lineswitch associated with each of said lines,

usr

f a trunk line, a group of primary line relays, a

group of secondary line relays, each of said lines being normally associated with a certain one oi said'primary linerelays andwith a cert-ain one of said secondary line relays, Yno two lines being associated with thesan'ie two relays, means 'effective when a call is initiated over one of said lines for operating the associated primary line relay, a self-locking circuit for the operated primary line relay, means effective when said self-locking circuit is closed for causing the operation of the secondary line relay associ-ated with the calling line and for disassociating the remaining primary line relays from said lines, and means in each lineswitch jointly controlled by the associated primary line relay and secondary line relay for connecting the associated line to said trunk line.

10. In a telephone system, a group o lines,

a group of trunks, a preselecting lineswitch terminating each of said lines :tor connecting the associated line to the preselected one of said trunks upon the initiation of acall, and a group of line relays less in number than the number of lines in said' group for controlling the operation of all of said lineswitches.

11. In a telephone system, a group of lines, a group of trunks, a lineswitch terminating each of said lines for connecting the associat ed line to one of said trunks responsive to the initiation of a call over the associated line, a groupof common line relays for said lines, each line being associated with a different two of said relays, and means controlled by the two relays associated with one oi' two lines over which calls are initiated simultaneouslyV o r nearly so for preventing` the two lines from being connected to the same trunk.

12. In a telephone system, a group of lines, a group of trunks, a lineswitch terminating each ofsaid lines V:tor connecting the associated line to the trunk opposite which the lineswitch is standing responsive to the initiation of a call over the associated line, theidle ones ot said lineswitches always being positioned opposite the same idle trunk, and moved to the next idle trunk when alineswitch is ope ated, and means for Jreventing two lineswitches from connecting their associated linesl to the samel trunk when calls areV initiated over the said associatedylines simultaneously or nearly so.

13. ln a telephone system, a group of lines, a group of trunks, a lineswitch terminating each of said lines for connecting the associated line to the trunk opposite which the lineswitch is standing responsive to the Vinitiation of a call over the associated line, the idle ones of said lineswitches always being positioned opposite the same idle trunk, and moved to the next idle trunk Vwhen a lineswit-ch is operated, and means 'for causing two lineswitches to operate successivelyto connect theirgassociated lines to different trunks even though calls are initiated over the said associated lines simultaneously or nearly so.

111-. In a telephone system, a group ot lineswitches, an operating magnet foreach lineswitch, a battery, and a group ot common line relays for connecting the poles of said battery to the magnets of said lineswitches.

1.5. In a telephone system, a group of lineswitches, an operating magnet for each lineswitch, a battery, a group oi common line relays for connecting'one poleot` said battery to one terminal ot' said magnets, and another group ofcommon line rela-ys for connecting the other pole of said battery to the other terminal of said magnets.

16. In a telephone system, a group of lineswitches, each lineswitchhaving an operating magnet,a group of common line relays for controlling the operation of said magnets, each lineswitch being normally connected to certain of said line relays, and contacts on each magnet for disconnecting the line relays normally connected to the lineswitch with which the magnet is associated.

17. ln a telephone system, a group of lines, each line terminating in alineswitch, a first Vand a second group of line relays, the total number of relays in the two groups being less than the number of lines insaid group, a relay.

oi the firstgroup being normally connected to one side of each line, and a relay of the second group beingnormally connected to the other side ot each line, and means controlled by the Y two-relays connected to'the two sides of a line when a call is initiated over the line for operating the lineswitch of the line.

.RUDOLPH F.V STEHLIK. 

